1. Field of the Invention
Aspects of the present invention relate to an organic light emitting display device (OLED) and a method of fabricating the same, and more particularly, to an OLED in which a cathode is replaced with a charge generation layer, and a method of fabricating the same.
2. Description of the Related Art
An OLED is a display device that uses a phenomenon in which an electron and a hole are injected into an organic layer through a cathode and an anode, and are recombined to generate an exciton, to thereby emit light with a specific wavelength. The OLED has advantages of a wide viewing angle, high brightness, and improved implementation of motion pictures due to a response time that is 30,000 times faster than recently commercialized liquid crystal display device (LCD). The OLED has a stacked structure capable of increasing an emission efficiency of light by the recombination of electrons and holes.
FIG. 1 is a cross-sectional view of a typical inverted type OLED. Referring to FIG. 1, a buffer layer 105 is formed on a substrate 100, and an amorphous silicon layer (not shown) is formed on the buffer layer 105, which is then crystallized into a polycrystalline silicon layer (not shown).
The polycrystalline silicon layer is patterned to form a semiconductor layer 110, and a gate insulating layer 115 is formed on an entire surface of the substrate 100 having the semiconductor layer 110. A gate electrode 120 is formed in a region of the gate insulating layer 115, which corresponds to the semiconductor layer 110. A photoresist pattern (not shown) is disposed on the gate electrode 120 as a mask, and then a source region 111, a drain region 113, and a channel region 112 are formed in the semiconductor layer 110 by performing an ion doping process.
An interlayer insulating layer 125 is formed on the entire surface of the substrate 100 having the gate electrode 120. Afterwards, the gate electrode 120 and the interlayer insulating layer 125 are etched, to thereby form a contact hole 125a to expose the source region 111 and the drain region 113. Source and drain electrodes 130 are respectively formed through the contact hole 125a so as to be connected with the source region 111 and the drain region 113.
A passivation layer 135 is formed on the entire surface of the substrate 100 having the source and drain electrodes 130, and a planarization layer 145 is formed on the passivation layer 135. The passivation layer 135 and the planarization layer 145 are etched to form a via hole 145a. A cathode 140 is formed on the planarization layer 145 and is connected to the source and drain electrodes 130 through the via hole 145a. 
A pixel defining layer 155 is formed on the cathode 140, and then etched, to thereby form an opening 155a which exposes a part of the cathode 140. An organic layer 160 including an emission layer is formed on the entire surface of the substrate 100, and includes the opening 155a. An anode 170 is formed on the organic layer 160. Thus, the inverted type OLED is formed.
However, the typical inverted type OLED of FIG. 1 has a problem in which a cathode formed of an alkali metal or an alkali earth metal (having a low work function) is easily oxidized when an anode is formed of ITO or IZO (by sputtering). To overcome this problem, the cathode has to be formed of a material having the same work function as the anode and a strong oxidation resistance. However, it is very difficult to accomplish such requirements with current technology.